Polycarbonate-polysiloxane copolymers and methods for preparing the same have been widely studied for many years. In general, polycarbonate-polysiloxane copolymers have been prepared by interfacial polymerization processes. For example, U.S. Pat. No. 5,530,083 discloses a method for preparing a silicone polycarbonate block copolymer using an interfacial phosgenation reaction in which an aromatic dihydroxy compound, phosgene and a catalyst are reacted with a hydroxyaryl terminated polydiorganosiloxane. However, this method uses a chlorinated solvent that is harmful to the environment.
U.S. Pat. No. 4,994,532 discloses a process of preparing a polycarbonate-silicone block copolymer by melt-blending a polycarbonate resin and a polydimethylsiloxane having a functional carboxylic acid group. In addition, U.S. Pat. No. 5,194,524 discloses a process for producing a copolymer by melt-mixing siloxane compounds having at least one secondary amine group and polycarbonate resins through a conventional extruder. According to the '524 patent, the polysiloxane having a secondary amine group is more effective for the reactive extrusion than a polysiloxane having a primary amine group, due to relatively low hydrolytic stability of primary amines.
Methods using a melt mixing process have some advantages, such as the use of a conventional melt extruder and a simple process. The resultant copolymers, however, can have low impact strength at low temperatures and low mechanical strength.